/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.object;

import org.springframework.lang.Nullable;

import javax.sql.DataSource;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Map;

/**
 * Reusable query in which concrete subclasses must implement the abstract
 * mapRow(ResultSet, int) method to convert each row of the JDBC ResultSet
 * into an object.
 *
 * <p>Simplifies MappingSqlQueryWithParameters API by dropping parameters and
 * context. Most subclasses won't care about parameters. If you don't use
 * contextual information, subclass this instead of MappingSqlQueryWithParameters.
 *
 * @param <T> the result type
 * @author Rod Johnson
 * @author Thomas Risberg
 * @author Jean-Pierre Pawlak
 * @see MappingSqlQueryWithParameters
 */
public abstract class MappingSqlQuery<T> extends MappingSqlQueryWithParameters<T> {

    /**
     * Constructor that allows use as a JavaBean.
     */
    public MappingSqlQuery() {
    }

    /**
     * Convenient constructor with DataSource and SQL string.
     *
     * @param ds  the DataSource to use to obtain connections
     * @param sql the SQL to run
     */
    public MappingSqlQuery(DataSource ds, String sql) {
        super(ds, sql);
    }


    /**
     * This method is implemented to invoke the simpler mapRow
     * template method, ignoring parameters.
     *
     * @see #mapRow(ResultSet, int)
     */
    @Override
    @Nullable
    protected final T mapRow(ResultSet rs, int rowNum, @Nullable Object[] parameters, @Nullable Map<?, ?> context)
            throws SQLException {

        return mapRow(rs, rowNum);
    }

    /**
     * Subclasses must implement this method to convert each row of the
     * ResultSet into an object of the result type.
     * <p>Subclasses of this class, as opposed to direct subclasses of
     * MappingSqlQueryWithParameters, don't need to concern themselves
     * with the parameters to the execute method of the query object.
     *
     * @param rs     the ResultSet we're working through
     * @param rowNum row number (from 0) we're up to
     * @return an object of the result type
     * @throws SQLException if there's an error extracting data.
     *                      Subclasses can simply not catch SQLExceptions, relying on the
     *                      framework to clean up.
     */
    @Nullable
    protected abstract T mapRow(ResultSet rs, int rowNum) throws SQLException;

}
